Checksum.
16 bits.
Checksum that covers the ICMPv6 message.
This field contains the 16-bit one's complement of the one's complement sum of the entire ICMPv6 message starting with the ICMPv6 message
type field, prepended with a pseudo-header of IPv6 header fields.
The pseudo-header contains the following fields:

00

01

02

03

04

05

06

07

08

09

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

Source IPv6 address :::

Destination IPv6 address :::

Upper layer packet length

0

Next header

ICMPv6 message.
Variable length.
Contains the data specific to the message type indicated by the Type and Code fields.